Blender Cycles Viewport Preview taking too long
This seems like a question about the performance of your specific components, which the Blender Stack Exchange is not able to help with as much.
You can reduce the viewport sample number (the default is 16) to shorten the time that it take to render (as you mentioned you did). You can also reduce the render samples and/or resolution of the camera to speed up the rendering process for rendering a final image or animation.
Here are a few things that may be causing slow viewport rendering times (not an exhaustive list):

Scenes with lots of objects and textures (remove any objects if possible)
Objects with high vertex/face count (use the minimum number of vertices possible)
High resolution textures on objects
Other applications using processor(s) in the background.

You can try fixing any of the above problems, edit using solid or material preview mode, and/or do your editing and modeling in Eevee before doing final edits and renders in Cycles.